The aim of this study is to describe postural reflexes in the neck and forelimbs resulting from the stimulation of the otolith organs in the vestibular labyrinth. Such "gravity" reflexes are involved in the maintenance of stable head and body position. The study seeks the answer to the following questions -- how do neck and limb muscles respond to various forms of otolith stimulation, what type of processing takes place in the vestibular nuclei, and what role do the vestibulospinal tracts play in the production of these reflexes. To answer these questions, experiments will be performed on decerebrate cats whose semicircular canals have been rendered nonfunctional by a plugging procedure, leaving only the otolith organs operative. Natural stimulation will be provided by a computer-controlled tilt table which can execute roll and pitch movements. Both muscle EMG activity and the firing of identified brainstem neurons in the vestibular nuclei will be recorded, and their modulation analyzed with respect to the tilt stimulus. By correlating the behavior of vestibular neurons with their location in the brainstem, their projection level and tracts in the spinal cord, and their input from the labyrinth, we hope to understand the role of this system in the production of the observed postural responses.